Basic protein purification tags from thermophilic bacteria

ABSTRACT

The invention is related to a method for purification of recombinant proteins using highly basic proteins from thermophilic bacteria as purification tags for use in a cation-exchange chromatography purification step. The basic proteins may be ribosomal proteins. The recombinant proteins are expressed in eukaryotic or prokaryotic host cells. The purification tag will typically have a pl above about 9 and comprise from about 15 to about 250 amino acid residues.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 11/911,563, filed Oct. 15, 2007 which is a 35 U.S.C. §371 nationalstage application of International Patent Application PCT/EP2006/061493(published as WO 2006/108826), filed Apr. 10, 2006, which claimedpriority of Danish Patent Application PA 2005 00549, filed Apr. 15,2005; this application further claims priority under 35 U.S.C. §119 ofU.S. Provisional Application 60/675,054, filed Apr. 26, 2005.

FIELD OF THE INVENTION

The present invention is related to a method of purifying recombinantproteins by use of a certain group of positively charged tags derivedfrom thermophilic bacteria.

BACKGROUND OF THE INVENTION

Purification of native or non-native recombinant proteins from bacterialor eukaryotic cells often requires several steps. Methods to reduce thenumber of steps in a purification of a target protein are advantageousfor cheap and efficient production of recombinant proteins. Purificationof target proteins fused to small highly basic domains is disclosed byGraslund et al., Protein Eng. 2000, 13(10):703-709, Graslund et al., JChromatogr A. 2002, 942(1-2):157-166 and Graslund et al., Journal ofBiotechnology, 2002, 96: 93-102. These publications describe therational design of highly basic and stable mutants of the Z-domain fromS. aureus protein A to purify different target proteins expressed in E.coli using cation-exchange chromatography. Use of highly basicderivatives of the Z-domain as fusion tags is also disclosed in WO00/6343.

The present invention provides a new group of positively charged tagswhich can be used to purify recombinantly expressed proteins to veryhigh purity in few steps.

SUMMARY OF THE INVENTION

In one aspect the invention is related to a method for purification ofrecombinant proteins comprising use of highly basic proteins fromthermophilic bacteria as purification tags in a cation-exchangechromatography purification step.

In one embodiment the purification tag has a pl above about 9.

In another embodiment the purification tag has a pl above about 10.

In another embodiment the pl of the purification tag will be betweenabout 9 and about 12.5 and in a further aspect the pl is about 10.

In one embodiment the highly basic proteins from the thermophilicbacteria are ribosomal proteins.

In one embodiment the purification tag contains no cysteine residues.

In a further embodiment the purification tag comprises from about 15 toabout 250, from about 15 to about 225, from 15 to about 200, from about15 to about 175, from about 15 to about 150, from 15 to about 75, orfrom about 15 to about 50 amino acid residues.

In a further embodiment the purification tag comprises from about 20 toabout 120, from about 20 to about 100, from about 20 to about 90, fromabout 20 to about 75 amino acid residues or from about 20 to about 50amino acid residues.

The purification tag will typically contain from at least about 15%basic amino acid residues and the purification tag may contain fromabout 20 to about 50%, from about 35% to about 50%, from about 20 to 30%or from about 40% to about 60% basic amino acid residues, Lys and Arg.

In another aspect the thermophilic bacteria are selected fromarchaebacteria or eubacteria which have growth optimum temperatureshigher than about 50° C.

In one embodiment the tag will comprise a linker sequence whichcomprises a cleavage site for in vitro cleavage of the purification tagto give the target protein.

In another embodiment the tag is remaining on the protein afterpurification.

The linker may have from 1-30, from 1-25, from 1-20 or from 1-15 aminoacid residues and in one embodiment the linker may comprise amino acidresidues such as Leu, Pro and Ala, which increases alpha helix formationor other features resulting in structural rigidity.

The linker may be attached to either the C-terminal or the N-terminalend of the target protein.

The cleavage site may be any cleavage site which enables in vitrocleavage of the purification tag from the target protein.

Non limiting examples of cleavage sites are an enterokinase cleavagesite, a Factor Xa cleavage site, a thrombin cleavage site, a Tobacco etcvirus (TEV) protease cleavage site or a HRV14 3C protease cleavage site.

In one embodiment the linker may have a peptide sequence selected fromthe group consisting of RRGGSDDDDK (SEQ ID NO:6); SSSDDDDK (SEQ IDNO:7); SSSSTSSSSTDDDDK (SEQ ID NO:8); SSSSTLAAPFDDDDK (SEQ ID NO:9)ALAAPFDDDDK (SEQ ID NO:15), SSSSDDDDK (SEQ ID NO:16), SSSSSLEVLFQ (SEQID NO:17), SSSALAAPADDDDK (SEQ ID NO:18), SSSSENLYFQ (SEQ ID NO:19)

In another aspect the present invention is related to a method formaking a recombinant protein comprising i) expression of a proteincomprising an N-terminal or C-terminal purification tag derived from ahighly basic protein from a thermophilic bacteria in a suitableexpression host, ii) loading the protein on a cation-exchange column,and iii) eluting the protein with a suitable eluent.

In one embodiment the highly basic proteins are ribosomal proteins.

In a further aspect the method according to the invention will comprisea cleavage step iv) wherein the purification tag is cleaved off to givethe target protein.

In one embodiment the cleavage step iv) is an enzymatic cleavage.

In a still further aspect the method according to the invention willcomprise a heat precipitation step for precipitating host cellcontaminants before the cation-exchange column step or at a later stepeg. after enzymatic cleavage of the purification tag to precipitate thecleavage enzyme.

In one embodiment from about 30 to about 200 mM NaCl is added before theheat precipitation step.

In another embodiment from about 30 to about 100 mM NaCl is added beforethe heat precipitation step.

In another embodiment from about 30 to about 50 mM NaCl is added beforethe heat precipitation step.

In one embodiment the expression host is selected from bacteria andfungi such as Eschericia species, Bacillus species, Saccharomycesspecies and Aspergillus species, in particularly Eschericia species andBacillus species.

In another aspect of the invention the purification tag is selected fromthe group of peptide sequences consisting of

(SEQ ID NO: 1) MSKTIVRKNESIDDALRRFKRAVSKTGTLQEVRKREFYEKPSVRRKKKSEAARKRK; (SEQ ID NO: 2)MGKKTVGVKKRLAKAYKQNRRAPVWITVKTKRSVFGSPKRRHWRRS KLKV; (SEQ ID NO: 3)MKRTYQPSRRKRKRTHGFLARKRTPGGRRVLKNRRRKGRWRLTV; (SEQ ID NO: 4)MGKGDRRTRRGKIWRGTYGKYRPRKKK and (SEQ ID NO: 5)MAKVKMKTNRSAAKRFKVTAKGKIKRWKSGGAHYNTKKSSKRKRHL RKHTYVKDNMLKHVKALLKEF.

In another aspect of the invention the purification tag is selected fromthe group of peptide sequences consisting of

(SEQ ID NO: 20) MPKHSKRYLEARKLVDRTKYYDLDEAIELVKKTATAKFDETIELHIQTGIDYRKPEQHIRGTIVLPHGTGKEVKVLVFAKGEKAKEALEAGADYVGAEDLVEKIEKEGFLDFDVAIATPDMMRIIGRLGKILGPRGLMPSPKSGTVTQEVAEAVKEFKKGRIEVRTDKTGNIHIPVGKRSFDNEKLKENIIAAIKQIMQMKPAGVKGQFIKKVVLASTMGPGIKLNLQSL LKE, (SEQ ID NO: 21)MAQVDLLNVKGEKVGTLEISDFVFNIDPNYDVMWRYVDMQLSNRRAGTASTKTRGEVSGGGRKPWPQKHTGRARHGSIRSPIWRHGGVVHGPKPRDWSKKLNKKMKKLALRSALSVKYRENKLLVLDDLKLERPKTKSLKEILQNLQLSDKKTLIVLPWKEEGYMNVKLSGRNLPDVKVIIADNPNNSKNGEKAVRIDGLNVFDMLKYDYLVLTRDMVSKIEEVLGNEAG KALTA, (SEQ ID NO: 22)MRYEYVPLKDQYEKEIVPALMKEFNYKNIHQVPKLVKIVINMGIGEGSRNYDLIERHANELAKITGQKPIVTRARKSISNFKIRKGMPIGLKVTLRGARMYNFLYKLINIVLPKVRDFRGLDPNSFDGRGNYSFGLSEQLVFPELNPDEVRRIQGMDITIVTTAKTDQEARRLLELFGMPFKRG, (SEQ ID NO: 23)MSRLAKKPIVLPQGVTVEIKDNVVKVKGPKGELSQEFLPYVKIEVEGNEVVVVRPNEEQIIRKSDWRKVKMFQGTYWSLIRNMVVGVTEGYKKELEIVGIGYRAQLQGNTLVMNLGYAHPVVYEIPSDVKIEVPAPNRIIVSGIDKQRVGQVAAEIRAFRPPNVYTGKGIRYVGEWRQKEGKKA, (SEQ ID NO: 24)MKVILLRDVPKIGKKGEIKEVSDGYARNYLIPRGFAKEYTEGLERAIKHEKEIEKRKKEREREESEKILKELKKRTHVVKVKAGEGGKIFGAVTAATVAEEISKTTGLKLDKRWFKLDKPIKELGEYSLEVSLPGGVK DTIKIRVEREE,(SEQ ID NO: 25) MLTRQQKELIVKEMSEIFKKTSLILFADFLGFTVADLTELRSRLREKYGDGARFRWKNTLLNLALKNAEYEGYEEFLKGPTAVLYVTEGDPVEAVKIIYNFYKDKKADLSRLKGGFLEGKKFTAEEVENIAKLPSKEELYAMLVGRVKAPITGLVFALSGILRNLVYVLNAIKEKKSE, (SEQ ID NO: 26)MARYFPVQKTTMIKPEEVERKVVYVVDASGKVLGRLATRIAKILMGKHKPNYTPHVDTGDYVIWNADKWLTGKKLDQKVYYWHSGYPGGLKSLTARQMLEKHPERLIWLAVKRMLPKNRKGRKMLKRLKVYASPEHPH QAQKPEPIEL,(SEQ ID NO: 27) MRLEDLRPTPGAMKKRKRVGRGPGSGHGKTSGRGHKGQKARGSGKVHIWFEGGQTPLQRRLPKRGFKNINKKVYAVVNVKVLEERFEANEEVTPEKLIERKIIKDLKDGVKILGDGELTKPLVVKAHAFSKSAVEKIE SAGGKAEVI,(SEQ ID NO: 28) MRHRVKRHKLGRYGSHRKSLLRNLSREIVEHGSIVTTTAKAKALKTFMDKLVSKAIEAATTDDRARSVHLRRQINAVLGDRRLTNKLVDEIAKNYVGRRGGYVRVLRIGFRRGDAAEMSLVQLVEASSQEG, (SEQ ID NO: 29)MDHLVKIIEKKYEKKEIPDFRPGDTVRVHVKVIEGDRERTQVFEGIVIAKRGSGINKTFTVRRIGSHGVGVERIFPVHSPVVEKIEVVRKGK VRRAKLYYLRNVRGKIRIKERRD,(SEQ ID NO: 30) MRVKRAVHAKKKRKKYLKAAKGYRGALSRRYKLAKQMYVRSKWYSYVGRKQKKRDMRKLWITRINIAARNEGLKYSELIHGLKLAGVSINRKMLSELAVNDPEAFKEYVKIAKEALAS, (SEQ ID NO: 31)MLYAIVETAGRQYRVEEGKILYTEKQKDYSPGDEIVFDRVVFVRKDGEVLVGKPYVEGAKVVGKVLEHAKARKVKTVKYRPRKNSKVEKGHR QVVYTAIKIEKIEL,(SEQ ID NO: 32) MKQEKLSLHDVLIRPIITEKALILREQRKYVFEVNPLANKNLVKEAVEKLFNVKVEKVNILNMKPKPKRRGIFEGKTRSWKKAVVTLKEGYT IKELEGEH, (SEQ ID NO: 33)MAHKKSGGVAKNGRDSLPKYLGVKVGDGQIVKAGNILVRQRGTRFYPGKNVGMGRDFTLFALKDGRVKFETKNNKKYVSVYEE, (SEQ ID NO: 34)MKASELRNYTDEELKNLLEEKKRQLMELRFQLAMGQLKNTSLIKLT KRDIARIKTILRERELGIRR,(SEQ ID NO: 35) MPKKLKIKLVKSPIGYSWDQKDTVKRLGLKKLNQVVIKDDLPQIRGMIRKVKHLVEVEEIEEGGSNA, (SEQ ID NO: 36)MKRTYQPSRRKRKRTHGFLARKRTPGGRRVLKNRRRKGRWRLTV, (SEQ ID NO: 37)MPKVKTNRSAAKRFRITKNGKIMRNHAYRSHKTGKKRRNALRALRK KDVVSSADKNRVLRLLGKK,(SEQ ID NO: 38) MGQKVHPRGFRLGLSADWQAKWFNEKNYKEWLLEDEEIRKIIKNKYYHAGISEIYVERPDAERINITVKTARPGIIIGRKGSEITSLREELERKFNRRVVINIEEIKTPELDAQLVAESIASRIEKRASYKVAMKRAIMNAMRKGAQGIKVMVAGRLGGAEIARREVVYLRGRLPLQKIKAIIDYGTATAWTKYGTIGIKVWIYKGDADI, (SEQ ID NO: 39)METQGVMKEIQYEEFEEKIIEIRRTSKVTKGGKNLSFRVVAIVGNKNGKVGLGIGKAREVPEAIRKAISAAKRNIVEVPVINGTIPHEVIGRQDASKVLLKPAAPGTGIIAGGTVRAVVELAGIQNILTKSLGSTNPLNLALATMNGLKNLLDPRKVAKLRDISVEEVFKGVRRENNA, (SEQ ID NO: 40)MVSLDPEKKNEIIKEFQIHENDTGSVEVQIALLTARIKHLTEHLRKHPKDFHSRRGLMKMIGRRRKMLKYLRHKKPEVYRELIAKLGIRK, (SEQ ID NO: 41)MGRSRKKGPYVDRKLLEKIRKLNETGEKKVIKTWSRASMIIPEMVGHTIAVYNGMKHIPVYITENMIGHRLGEFAPTRRFGGHADKKAKKGE LKK and (SEQ ID: NO 42)MPNIKSAKKRVRVSEKRRLRNKAYKTFFKNRIKEVLKAIENKEPKEVVLELTRKAQAAIDKAVSKGVIHKNQGARRKARLFEKVNEYLRTLE TTQE.

In another embodiment the purification tag is selected from the groupconsisting of

(SEQ ID NO: 32) MKQEKLSLHDVLIRPIITEKALILREQRKYVFEVNPLANKNLVKEAVEKLFNVKVEKVNILNMKPKPKRRGIFEGKTRSWKKAVVTLKEG YTIKELEGEH and(SEQ ID NO: 33) MAHKKSGGVAKNGRDSLPKYLGVKVGDGQIVKAGNILVRQRGTRFYPGKNVGMGRDFTLFALKDGRVKFETKNNKKYVSVYEE.

The target protein will typically be of a size from about 20 to about400 amino acid residues, more typically from about 30 to about 400 aminoacid residues or from about 30 to about 400 amino acid residues.

In a further aspect of the invention the target protein is selected fromhuman proteins and their analogues such as aprotinin, tissue factorpathway inhibitor or other protease inhibitors, insulin or insulinanalogues, human or bovine growth hormone, interleukin, glucagon, GLP-1,GLP-2, IGF-I, IGF-II, tissue plasminogen activator, transforming growthfactor α or β, platelet-derived growth factor, GRF (growth hormonereleasing factor), immunoglubolines, EPO, TPA, protein C, bloodcoagulation factors such as FVII, FVIII, FIV and FXIII, exendin-3,exentidin-4, and enzymes or functional analogues thereof.

DESCRIPTION OF THE DRAWINGS

FIG. 1 discloses an expression vector pNNC20 comprising the followingelements; lacl coding sequence, ampicillin (bla) coding sequence, pBR322origin of replication, T7 promoter region, T7 terminator region, SEQ IDNO:1 purification tag, RRGGSDDDDK (SEQ ID NO:6) linker region and maturehuman hGH sequence;

FIG. 2 discloses two non-reducing SDS-PAGE gel images of fractions 23-47collected from the main NNC20 peak from purification on AKTA explorerdescribed in example 1, where M is Protein marker, Appl. is NNC20Application and Ft is Flow through. Arrow indicates position of elutedfusion protein.

FIG. 3 discloses the chromatogram of a NNC20 where FIG. 3A shows thepurification described in example 1 and FIG. 3B shows the chromatogramof an hGH fusion protein purification described in example 2. Arrowspoint at the main peak containing the eluted fusion protein. Stippledcurves indicate the conductivity (milli Siemens/cm) measured during thegradient formed by adding NaCl. Solid lines indicate the UV280 measuredduring the purification.

FIG. 4 discloses the chromatogram from purification of ACSH200 describedin example 4 (4A), the corresponding SDS PAGE gel of the collectedfractions (4B) (arrows point at eluted ACSH200 fusion protein) and theextracted deconvoluted MS spectrum from analysis of fraction 25 (4C)showing the mass of the intact ACSH200 fusion protein described inexample 4.

FIG. 5 discloses the SDS PAGE gel of supernatants with different NaClconcentration that were heat treated in a precolumn purification step asdescribed in Example 5 where M is Protein marker. Arrow points atACSH200 fusion protein. M: marker, 0-1000 mM NaCl added to the samples,Ctrl is a non heated control.

FIG. 6 discloses an LC-MS analysis of purified and EK digested ACSH204fusion protein.

FIG. 6A discloses TIC chromatogram of enzymatic cleavage of pACSH204showing total ions eluted from a Poroshell SB300 C8 (AgilentTechnologies) column, Peak 1: Human Amylin, Peak 2: Purification tagreleased with EK, Peak 3: intact fusion protein, Peak 4: fragment due tounknown E. coli protease cleaving after 6 amino acid residues in Amylin

FIG. 6B discloses extracted spectrum of Peak 1 comprising the releasedhuman Amylin peptide

FIG. 6C discloses extracted and deconvoluted spectrum of Peak 2comprising the released purification tag and

FIG. 6 D discloses:extracted and deconvoluted spectrum of Peak 4comprising the intact uncleaved ACSH204

DESCRIPTION OF THE INVENTION

Strains of thermophilic bacteria have been identified with optimumtemperatures ranging from −50° C. to above the boiling point of water.The strains that survive at extremely high temperatures are calledhyperthermophiles or thermophiles and have a temperature optimum of 80°C. (176° F.) or higher. Thermophilic bacteria occur naturally in hotsprings, hot soils, geothermal vents and other places were hightemperature are present. Bacillus stearothermophillus from whichRS21_BACST (SEQ ID NO:1) was cloned and used as a tag is for examplefound to grow above 65° C. in many soils. In order to survive the hightemperatures, these organisms have evolved proteins which are morestable than those of mesophiles.

The purification tags according to the present invention are derivedfrom thermophilic bacteria and are in general soluble, highly stable andhave a very basic pl due to a large amount of Arg and Lys residuespresent in the amino acid sequence. The solubility is believed to bederived from the generally high surface charge of the proteins. Thepurification tags according to the present invention comprise a highpercentage of positively charged amino acid residues Lys and Arg.

Representative examples of species comprising thermophiles areAcetomicrobium sp., Acidianus sp.; Acremonium sp.; Actinopolyspora sp.;Aeropyrum sp.; Alicyclobacillus sp., Ammonifex sp.; Amycolatopsis sp.;Anaerobaculum sp.; Anaerobranca sp.; Anaerocellum sp.; Aneurinibacillussp.; Anoxybacillus sp.; Aquifex sp.; Archaeoglobus sp.; Bacillus sp.;Brevibacillus sp.; Caldicellulosiruptor sp.; Caldithrix sp.; Caldivirgasp.; Caloramator sp.; Caloranaerobacter sp.; Caminibacter sp.;Carboxydothermus sp.; Chaetomium sp.; Chlorobaculum sp.; Chloroflexussp.; Clostridium sp.; Coprothermobacter sp.; Deferribacter sp.;Deinococcus sp.; Desulfacinum sp.; Desulfotomaculum sp.; Desulfurellasp.; Desulfurococcus sp.; Dictyoglomus sp.; Ferroglobus sp.;Fervidobacterium sp.; Gelria sp.; Geobacillus sp.; Halorhodospira sp.;Halothermothrix sp.; Heliobacterium sp.; Hippea sp.; Hydrogenobactersp.; Hydrogenophilus sp.; Hyperthermus sp.; Malbranchea sp.; Marinitogasp.; Meiothermus sp.; Metallosphaera sp.; Methanobacterium sp.;Methanocaldococcus sp.; Methanoculleus sp.; Methanohalobium sp.;Methanopyrus sp.; Methanosarcina sp.; Methanothermobacter sp.;Methanothermococcus sp.; Methanothermus sp.; Methanothrix sp.;Methanotorris sp.; Microbispora sp.; Moorella sp.; Myceliophthora sp.;Nautilia sp.; Palaeococcus sp.; Pelotomaculum sp.; Persephonella sp.;Petrotoga sp.; Picrophilus sp.; Pseudomonas sp.; Pseudonocardia sp.;Pyrobaculum sp.; Pyrococcus sp.; Pyrodictium sp.; Rhizomucor sp.;Rhizomucor sp.; Rhodothermus sp.; Roseiflexus sp.; Rubrobacter sp.;Saccharococcus sp.; Saccharomonospora sp.; Saccharopolyspora sp.;Scytalidium sp.; Spirochaeta sp.; Stetteria sp.; Streptomyces sp.;Stygiolobus sp.; Sulfobacillus sp.; Sulfolobus sp.; Sulfophobococcussp.; Sulfurihydrogenibium sp.; Syntrophothermus sp.; Tepidimonas sp.;Thermacetogenium sp.; Thermaerobacter sp.; Thermanaerovibrio sp.;Thermicanus sp.; Thermoactinomyces sp.; Thermoanaerobacter sp.;Thermoanaero-bacterium sp.; Thermoanaerobium sp.; Thermoanaeromonas sp.;Thermoascus sp.; Thermo-bifida sp.; Thermobrachium sp.; Thermochromatiumsp.; Thermococcus sp.; Thermodesulfo-vibrio sp.; Thermodesulfobacteriumsp.; Thermodesulforhabdus sp.; Thermo-filum sp.; Thermohydrogenium sp.;Thermomonospora sp.; Thermonema sp.; Therm-oplasma sp.; Thermoproteussp.; Thermosipho sp.; Thermosphaera sp.; Thermo-syntropha sp.;Thermo-terrabacterium sp.; Thermotoga sp.; Thermovenabulum sp.;Thermo-vibrio sp.; Thermus sp. and Ureibacillus sp.

The present purification method can be used to purify a large number ofproteins being produced by recombinant gene technology. The targetprotein is typically of small to medium size and may have up to about400 amino acid residues. The target proteins may be of a size from about30 to about 400 amino acid residues, from about 40 to about 400 aminoacid residues, from about 50 to about 400 amino acid residues, fromabout 60 to about 400 amino acid residues, from about 70 to about 400amino acid residues, from about 80 to about 400 amino acid residues,from about 90 to about 400 amino acid residues or from about 100 toabout 400 amino acid residues.

Further, the target protein may be of from about 30 to about 300 aminoacid residues, from about 40 to about 300 amino acid residues, fromabout 50 to about 300 amino acid residues, from about 60 to about 300amino acid residues, from about 70 to about 300 amino acid residues,from about 80 to about 300 amino acid residues, from about 90 to about300 amino acid residues or from about 100 to about 300 amino acidresidues.

Further, the target protein may be of from about 30 to about 200 aminoacid residues, from about 40 to about 200 amino acid residues, fromabout 50 to about 200 amino acid residues, from about 60 to about 200amino acid residues, from about 70 to about 200 amino acid residues,from about 80 to about 200 amino acid residues, from about 90 to about200 amino acid residues or from about 100 to about 200 amino acidresidues.

Further, the target protein may be of from about 30 to about 100 aminoacid residues, from about 40 to about 100 amino acid residues, fromabout 50 to about 100 amino acid residues, from about 60 to about 100amino acid residues, from about 70 to about 100 amino acid residues,from about 80 to about 100 amino acid residues or from about 90 to about100 amino acid residues.

Non limiting examples of such proteins are: aprotinin, tissue factorpathway inhibitor or other protease inhibitors, insulin or insulinprecursors, human or bovine growth hormone, interleukin, glucagon,GLP-1, GLP-2, IGF-I, IGF-II, tissue plasminogen activator, transforminggrowth factor α or β, platelet-derived growth factor, GRF (growthhormone releasing factor), immunoglubolines, EPO, TPA, protein C, bloodcoagulation factors such as FVII, FVIII, FIV and FXIII, exendin-3,exentidin-4, and enzymes or functional analogues thereof.

Other examples of target proteins are transforming growth factor α(TGF-α), transforming growth factor β (TGF-β), epidermal growth factor(EGF), vascular endothelial growth factor (VEGF), thrombopoietin (TPO),interferon, pro-urokinase, urokinase, plasminogen activator inhibitor 1,plasminogen activator inhibitor 2, von Willebrandt factor, a cytokine,e.g. an interleukin such as interleukin (IL) 1, IL-1Ra, IL-2, IL-4,IL-5, IL-6, IL-9, IL-11, IL-12, IL-13, IL-15, IL-16, IL-17, IL-18, IL-20or IL-21, a colony stimulating factor (CFS) such as GM-CSF, stem cellfactor, a tumor necrosis factor such as TNF-α, lymphotoxin-α,lymphotoxin-β, CD40L, or CD30L, a protease inhibitor e.g. aprotinin, anenzyme such as superoxide dismutase, asparaginase, arginase, argininedeaminase, adenosine deaminase, ribonuclease, catalase, uricase,bilirubin oxidase, trypsin, papain, alkaline phosphatase,β-glucoronidase, purine nucleoside phosphorylase or batroxobin, anopioid, e.g. endorphins, enkephalins or non-natural opioids, a hormoneor neuropeptide, e.g. calcitonin, glucagon, gastrins,adrenocorticotropic hormone (ACTH), cholecystokinins, lutenizinghormone, gonadotropin-releassing hormone, chorionic gonadotropin,corticotrophin-releasing factor, vasopressin, oxytocin, antidiuretichormones, thyroid-stimulating hormone, thyrotropin-releasing hormone,relaxin, prolactin, peptide YY, neuropeptide Y, pancreastic polypeptide,leptin, CART (cocaine and amphetamine regulated transcript), a CARTrelated peptide, perilipin, melanocortins (melanocyte-stimulatinghormones) such as MC-4, melanin-concentrating hormones, natriureticpeptides, adrenomedullin, endothelin, secretin, amylin, vasoactiveintestinal peptide (VIP), pituary adenylate cyclase activatingpolypeptide (PACAP), bombesin, bombesin-like peptides, thymosin,heparin-binding protein, soluble CD4, hypothalmic releasing factor andmelanotonins.

In another embodiment of the invention the target protein may be insulinreceptor agonist or antagonist peptides or other peptides designed tointeract with other cell membrane receptors

In another embodiment of the invention the target protein may be aprocessing enzyme such as proteases (eg enterokinase, caspases trypsinelike serine proteases), lipase, phospatase, glycosyl hydrolases (eg.mannosidases, xylosidases, fucosidases), kinase, mono or dioxidase,peroxidase, transaminase, carboxypeptidase, amidase, esterase, andphosphatase.

Thermostable proteins are often stabilized through salt bridging, byincreased number of hydrogen bonds and a very compact packing of thehydrophobic core. Thus, the structural integrity of proteins fromthermophilic bacteria is believed to be mediated via intra-molecularinteractions even in proteins without cysteine residues. The absence ofcysteine residues in a purification tag is advantageous as this willreduce the risk of interferences from cysteine residues in thepurification tag with disulphide bridges in the target protein andreduce the formation of insoluble disulphide linked aggregates duringprotein expression. The high charge of the purification tag will alsocontribute to the solubility of the fusion protein. The susceptibilityof a peptide bond to cleavage by a protease is determined by both theflexibility of the protein chain region in which it is located, theextent to which the bond is exposed, and how local interactions are madeby the side chains of its flanking residues. Each of these parameters isinfluenced by the overall structural stability of the protein. Thus, thestructural integrity of the purification tag according to the presentinvention will limit the potential degradation of the tag by trypsinlike proteases from the host cell used for production of the fusionprotein.

A number of tagged proteins were cloned and expressed E. coli. Thetagged proteins were expressed without significant degradation of thepurification tag and only very few contaminant peptides were found aftercleavage with trypsin. Thus, the tag has a high resistance towardstrypsin-like proteases and ensures effective cleavage of the expressedtagged protein. Furthermore, it was found that the purification tag didnot interfere with the establishment of the correct disulphide bridgesin the target protein.

In E. coli the majority of abundant proteins are found in a pl clusterranging from pl 4-7 and 8-10 in which the majority of the proteins aswell as the most abundant proteins are found in the pl 4-7 range. Thepurification tags according to the invention are highly alkaline andwill when fused to a target protein significantly increase the overallpositive charge and pl of the fusion protein so that it is clearlydistinguished from the major bulk of host cell contaminants. This willallow the fusion protein to be eluted at salt concentrations or at a plat which the host cell contaminants will not be able to bind to a givencation exchange matrix.

Any suitable cation exchange matrix can be used in the method accordingto the invention and a non limiting list of suitable cation exchangecolumn material is: SP-Sepharose XL Amersham cat no 17-5073-01;Streamline SP XL Amersham cat no 17-5076-01; Streamline Direct CSTAmersham cat no 17-5266-03; Obelix SP Amersham cat no 11-0010-86;S-Support Unosphere, BioRad cat no 156-0113; SP-Sepharose HighPerformance Amersham cat no 17-1087-03; Source30S Amersham cat no17-1273-02 and Toyopearl SP650S TosoHaas cat no 08437

The purification tags according to the invention will contributedifferently to the overall charge of a specific target protein dependingon the pl and charge of the chosen purification tag. Thus, purificationof a specific target protein can be optimized by choosing a purificationtag which enables elution of the fusion protein at a salt concentrationor at a pH at which only minimal amounts of the host cell contaminantswill co-elute.

The amino acid residues in the linker can be selected from such aminoacid residues which will provide a less flexible structure to the taggedprotein. Hereby the interference between the target protein and thepurification tag may be minimized. In one embodiment, the linker maycomprise structural elements such as alpha helix structure.

The expressed tagged or fusion proteins produced by the cells may berecovered from the culture medium by conventional procedures includingseparating the host cells from the medium by centrifugation orfiltration, releasing the fusion protein by mechanical cell disruption,such as ultrasonication or pressure, precipitating the proteinaqueouscomponents of the supernatant or filtrate by means of a salt, e.g.ammonium sulphate. Due to the thermostbility of the purification tagsaccording to the invention a prechromatographic step comprising a heatprecipitation of host cell contaminants is also possible, especially ifthe target protein is small in comparison to the fusion tag. Aftersonication a suitable concentration of NaCl can be added to furtherdecrease the ability of host cell contaminants to bind to the cationexchange matrix. After cation-exchange chromatography the fusion proteinmay be eluted in a salt gradient and eluate fractions containing thefusion protein were collected.

Purity of the fusion protein was evaluated by analyzing Coomasie stainedPAGE gels using gel image analysis software.

After the first purification step the purification tag can be cleavedoff directly with a suitable processing enzyme (eg. EK). If the saltconcentration is too high the fusion protein may be desalted beforecleavage. The cleavage site can be any cleavage site which will enableefficient in vitro cleavage after isolating the purified fusion protein.The most commonly used enterokinase cleavage site has the sequence DDDDK(SEQ ID NO:10), where cleavage occurs after K. Other non-limitingprocessing enzymes cleavage sites include the Factor Xa cleavage site,which is most commonly IEGR (SEQ ID NO:11), where cleavage occurs afterR; the thrombin cleavage site, which is most commonly LVPRG (SEQ IDNO:12) or LVPRGS (SEQ ID NO:13) where cleavage occurs after the R; theTobacco etcs virus (TEV) protease cleavage site, which is most commonlyENLYFQG/S (SEQ ID NO:14), where cleavage occurs after Q and the HRV14 3Cprotease cleavage site, which is most commonly LEVLFQ/GP where cleavageoccurs after Q.

The steps following cleavage may include a further cation exchangecolumn purification as in the first step. In such scenario thepurification tag released by the processing enzyme will have anextremely high pl leading to very efficient binding to the cationexchange matrix. The cleaved protein can now be collected in the flowthrough from the column, whereas the cleaved off purification tag andremaining highly charged contaminants from the production cell line willbe retained on the cation exchange column.

Purification steps following cleavage may also comprise other means ofpurification such as anion exchange chromatography, hydrophobicinteraction chromatography and gel filtration chromatography (see, forexample, Scopes, R., Protein Purification, Springer-Verlag, N.Y., 1982).

For therapeutic purposes the target protein has to be substantially pureafter the last purification step. Thus, in a preferred embodiment of theinvention the target protein is purified to at least about 90 to 95%homogeneity, preferably to at least about 98% homogeneity. Purity may beassessed by e.g. gel electrophoresis, amino acid analysis or other HPLCbased methods.

The nucleic acid construct encoding the fusion protein may suitably beof genomic or cDNA origin, for instance obtained by preparing a genomicor cDNA library and screening for DNA sequences coding for all or partof the fusion protein by hybridization using synthetic oligonucleotideprobes in accordance with standard techniques (cf. Sambrook et al.,Molecular Cloning: A Laboratory Manual, 2nd. Ed. Cold Spring HarborLabora-tory, Cold Spring Harbor, N.Y., 1989).

The nucleic acid construct encoding the fusion protein may also beprepared synthetically by established standard methods, e.g. thephosphoamidite method described by Beaucage and Caruthers, TetrahedronLetters 22 (1981), 1859-1869, or the method described by Matthes et al.,EMBO Journal 3 (1984), 801-805. According to the phosphoamidite method,oligonucleotides are synthesised, e.g. in an automatic DNA synthesiser,purified, annealed, ligated and cloned in suitable vectors. The DNAsequences encoding the fusion protein may also be prepared by polymerasechain reaction such as splicing by overlap extension PCR using specificprimers, for instance as described in U.S. Pat. No. 4,683,202, Saiki etal., Science 239 (1988), 487-491, or Sambrook et al., supra.

Furthermore, the nucleic acid construct may be of mixed synthetic andgenomic, mixed synthetic and cDNA or mixed genomic and cDNA originprepared by ligating fragments of synthetic, genomic or cDNA origin (asappropriate), the fragments corresponding to various parts of the entirenucleic acid construct, in accordance with standard techniques.

The DNA sequences encoding the fusion protein are usually inserted intoa recombinant vector which may be any vector, which may conveniently besubjected to recombinant DNA procedures, and the choice of vector willoften depend on the host cell into which it is to be introduced. Thus,the vector may be an autonomously replicating vector, i.e. a vector,which exists as an extrachromosomal entity, the replication of which isindependent of chromosomal replication, e.g. a plasmid. Alternatively,the vector may be one which, when introduced into a host cell, isintegrated into the host cell genome and replicated together with thechromosome(s) into which it has been integrated.

The vector is preferably an expression vector in which the DNA sequenceencoding the fusion protein is operably linked to additional segmentsrequired for transcription of the DNA. In general, the expression vectoris derived from plasmid or viral DNA, or may contain elements of both.The term, “operably linked” indicates that the segments are arranged sothat they function in concert for their intended purposes, e.g.transcription initiates in a promoter and proceeds through the DNAsequence coding for the fusion protein.

Expression vectors for use in expressing the fusion protein willcomprise a promoter capable of directing the transcription of a clonedgene or cDNA. The promoter may be any DNA sequence, which showstranscriptional activity in the host cell of choice and may be derivedfrom genes encoding proteins either homologous or heterologous to thehost cell.

Examples of suitable promoters for directing the transcription of theDNA in mammalian cells are the SV40 promoter (Subramani et al., Mol.Cell. Biol. 1 (1981), 854-864), the MT-1 (metallothionein gene) promoter(Palmiter et al., Science 222 (1983), 809-814), the CMV promoter(Boshart et al., Cell 41:521-530, 1985) or the adenovirus 2 major latepromoter (Kaufman and Sharp, Mol. Cell. Biol, 2:1304-1319, 1982).

Examples of suitable promoters for use in yeast host cells includepromoters from yeast glycolytic genes (Hitzeman et al., J. Biol. Chem.255 (1980), 12073-12080; Alber and Kawasaki, J. Mol. Appl. Gen. 1(1982), 419-434) or alcohol dehydrogenase genes (Young et al., inGenetic Engineering of Microorganisms for Chemicals (Hollaender et al,eds.), Plenum Press, New York, 1982), or the TPI1 (U.S. Pat. No.4,599,311) or ADH2-4-c (Russell et al., Nature 304 (1983), 652-654)promoters.

Examples of suitable promoters for use in filamentous fungus host cellsare, for instance, the ADH3 promoter (McKnight et al., The EMBO J. 4(1985), 2093-2099) or the tpiA promoter. Examples of other usefulpromoters are those derived from the gene encoding A. oryzae TAKAamylase, Rhizomucor miehei aspartic proteinase, A. niger neutralalpha-amylase, A. niger acid stable alpha-amylase, A. niger or A.awamori glucoamylase (gluA), Rhizomucor miehei lipase, A. oryzaealkaline protease, A. oryzae triose phosphate isomerase or A. nidulansacetamidase. Preferred are the TAKA-amylase and gluA promoters. Suitablepromoters are mentioned in, e.g. EP 238 023 and EP 383 779.

Examples of suitable promoters for use in bacterial host cells includethe promoter of the Bacillus stearothermophilus maltogenic amylase gene,the Bacillus licheniformis alpha-amylase gene, the Bacillusamyloliquefaciens BAN amylase gene, the Bacillus subtilis alkalineprotease gen, or the Bacillus pumilus xylosidase gene, or the phageLambda P_(R) or P_(L) promoters or promoters used for expression in E.coli eg. lac, trp, phoA, araBAD, tac, bacteriophage T7 and cspA.

The vector may also comprise a selectable marker, e.g. a gene productwhich complements a defect in the host cell, such as the gene coding fordihydrofolate reductase (DHFR) or the Schizosaccharomyces pombe TPI gene(described by P. R. Russell, Gene 40, 1985, pp. 125-130), or a markergene which confers resistance to a drug, e.g. ampicillin, kanamycin,tetracyclin, chloramphenicol, neomycin, hygromycin or methotrexate. Forfilamentous fungi, selectable markers include amdS, pyrG, arqB, niaD andsC.

The DNA sequences encoding the fusion protein may also, if necessary, beoperably connected to a suitable terminator, such as the human growthhormone terminator (Palmiter et al., Science 222, 1983, pp. 809-814) orthe TPI1 (Alber and Kawasaki, J. Mol. Appl. Gen. 1, 1982, pp. 419-434)or ADH3 (McKnight et al., The EMBO J. 4, 1985, pp. 2093-2099)terminators. Expression vectors may also contain a set of RNA splicesites located downstream from the promoter and upstream from theinsertion site for the fusion polypeptide sequence itself. Preferred RNAsplice sites may be obtained from adenovirus and/or immunoglobulingenes. Also contained in the expression vectors is a polyadenylationsignal located downstream of the insertion site. Particularly preferredpolyadenylation signals include the early or late polyadenylation signalfrom SV40 (Kaufman and Sharp, ibid.), the polyadenylation signal fromthe adenovirus 5 Elb region, the human growth hormone gene terminator(DeNoto et al. Nucl. Acids Res. 9:3719-3730, 1981). The expressionvectors may also include a non coding viral leader sequence, such as theadenovirus 2 tripartite leader, located between the promoter and the RNAsplice sites; and enhancer sequences, such as the SV40 enhancer.

To direct the fusion protein into the secretory pathway of the hostcells, a secretory signal sequence (also known as a leader sequence,prepro sequence or pre sequence) may be provided in the recombinantvector. The secretory signal sequence is joined to the DNA sequencesencoding the fusion protein in the correct reading frame. Secretorysignal sequences are commonly positioned 5′ to the DNA sequence encodingthe peptide. The secretory signal sequence may be that, normallyassociated with the protein or may be from a gene encoding anothersecreted protein.

For secretion from yeast cells, the secretory signal sequence may encodeany signal peptide, which ensures efficient direction of the expressedpolypeptides into the secretory pathway of the cell. The signal peptidemay be naturally occurring signal peptide, or a functional part thereof,or it may be a synthetic peptide. Suitable signal peptides have beenfound to be the alpha-factor signal peptide (cf. U.S. Pat. No.4,870,008), the signal peptide of mouse salivary amylase (cf. O.Hagenbuchle et al., Nature 289, 1981, pp. 643-646), a modifiedcarboxypeptidase signal peptide (cf. L. A. Valls et al., Cell 48, 1987,pp. 887-897), the yeast BAR1 signal peptide (cf. WO 87/02670), or theyeast aspartic protease 3 (YAP3) signal peptide (cf. M. Egel-Mitani etal., Yeast 6, 1990, pp. 127-137).

For efficient secretion in yeast, a sequence encoding a leader peptidemay also be inserted downstream of the signal sequence and upstream ofthe DNA sequence encoding the polypeptides. The function of the leaderpeptide is to allow the expressed peptide to be directed from theendoplasmic reticulum to the Golgi apparatus and further to a secretoryvesicle for secretion into the culture medium (i.e. exportation of thepolypeptides across the cell wall or at least through the cellularmembrane into the periplasmic space of the yeast cell). The leaderpeptide may be the yeast alpha-factor leader (the use of which isdescribed in e.g. U.S. Pat. No. 4,546,082, U.S. Pat. No. 4,870,008, EP16 201, EP 123 294, EP 123 544 and EP 163 529). Alternatively, theleader peptide may be a synthetic leader peptide, which is to say aleader peptide not found in nature. Synthetic leader peptides may, forinstance, be constructed as described in WO 89/02463 or WO 92/11378.

For use in filamentous fungi, the signal peptide may conveniently bederived from a gene encoding an Aspergillus sp. amylase or glucoamylase,a gene encoding a Rhizomucor miehei lipase or protease or a Humicolalanuginosa lipase. The signal peptide is preferably derived from a geneencoding A. oryzae TAKA amylase, A. niger neutral alpha-amylase, A.niger acid-stable amylase, or A. niger glucoamylase. Suitable signalpeptides are disclosed in, e.g. EP 238 023 and EP 215 594.

The host cell into which the DNA construct encoding the fusion proteinis introduced may be any cell which is capable of producing the presentfusion polypeptides and includes bacteria, yeast, fungi and highereukaryotic cells.

Examples of bacterial host cells which, on cultivation, are capable ofproducing the polypeptide of the invention are grampositive bacteriasuch as strains of Bacillus, such as strains of B. subtilis, B.licheniformis, B. lentus, B. brevis, B. stearothermophilus, B.alkalophilus, B. amyloliquefaciens, B. coagulans, B. circulans, B.lautus, B. megatherium or B. thuringiensis, or strains of Streptomyces,such as S. lividans or S. murinus, or gram negative bacteria such asstrains of Echerichia coli. The transformation of the bacteria may beeffected by protoplast transformation or by using competent cells in amanner known per se (cf. Sambrook et al., supra).

When expressing protein in bacteria such as E. coli, the protein may beretained in the cytoplasm, typically as insoluble granules (known asinclusion bodies), or may be directed to the periplasmic space by abacterial secretion sequence. In the former case, the cells are lysedand the granules are recovered and denatured after which the polypeptideis refolded by diluting the denaturing agent. In the latter case, thetarget protein may be cloned with a strong signal peptide sequence suchas phoA, degQ, degS, degP, OmpA, OmpF, OmpH, OmpP, OmpT, lamb or pelB(from Erwania carotovora) and the polypeptide may be recovered from theperiplasmic space by disrupting the cells, e.g. by sonication or osmoticshock, to release the contents of the periplasmic space and recoveringthe polypeptide.

Examples of suitable yeasts cells include cells of Saccharomyces spp. orSchizosac-charomyces spp., in particular strains of Saccharomycescerevisiae or Saccharomyces kluyveri. Methods for transforming yeastcells with heterologous DNA and producing heterologous poly-peptidesthere from are described, e.g. in U.S. Pat. No. 4,599,311, U.S. Pat. No.4,931,373, U.S. Pat. Nos. 4,870,008, 5,037,743, and U.S. Pat. No.4,845,075, all of which are hereby incorporated by reference.Transformed cells are selected by a phenotype determined by a selectablemarker, commonly drug resistance or the ability to grow in the absenceof a particular nutrient, e.g. leucine. A preferred vector for use inyeast is the POT1 vector disclosed in U.S. Pat. No. 4,931,373. The DNAsequences encoding the human polypeptides may be preceded by a signalsequence and optionally a leader sequence, e.g. as described above.Further examples of suitable yeast cells are strains of Kluyveromyces,such as K. lactis, Hansenula, e.g. H. polymorpha, or Pichia, e.g. P.pastoris (cf. Gleeson et al., J. Gen. Microbiol. 132, 1986, pp.3459-3465; U.S. Pat. No. 4,882,279).

Examples of other fungal cells are cells of filamentous fungi, e.g.Aspergillus spp., Neurospora spp., Fusarium spp. or Trichoderma spp., inparticular strains of A. oryzae, A. nidulans or A. niger. The use ofAspergillus spp. for the expression of proteins is described in, e.g.,EP 272 277, EP 238 023, EP 184 438 The transformation of F. oxysporummay, for instance, be carried out as described by Malardier et al.,1989, Gene 78: 147-156. The transformation of Trichoderma spp. may beperformed for instance as described in EP 244 234.

When a filamentous fungus is used as the host cell, it may betransformed with the DNA construct of the invention, conveniently byintegrating the DNA construct in the host chromosome to obtain arecombinant host cell. This integration is generally considered to be anadvantage as the DNA sequence is more likely to be stably maintained inthe cell. Integration of the DNA constructs into the host chromosome maybe performed according to conventional methods, e.g. by homologous orheterologous recombination.

The transformed or transfected host cell is then cultured in a suitablenutrient medium under conditions permitting expression of the fusionprotein after which all or part of the resulting peptide may berecovered from the culture. The medium used to culture the cells may beany conventional medium suitable for growing the host cells, such asminimal or complex media containing appropriate supplements. Suitablemedia are available from commercial suppliers or may be preparedaccording to published recipes (e.g. in catalogues of the American TypeCulture Collection).

DEFINITIONS

In the present context “Thermophilic microorganisms” means organismswhich grow optimally at about 50° C. to about 100° C. This is incontrast to mesophiles which in general grow optimally at temperaturesfrom 30-37° C. The term “thermophilic bacteria” will in this contextcover hyperthermophilic bacteria as well.

“Ribosomal proteins” are peptide or polypeptide subunits of the ribosomewhich are the particles that catalyze mRNA-directed protein synthesis inall organisms. Ribosomal proteins are defined on the basis of theirsequence by ribosomal signatures as reported in domain databases such asInterPro and Prosite.

“Recombinant protein” is a protein produced by recombinant productiontechnology.

The expression “purification tag” means a peptide sequence fused to atarget protein either at the N- or C-terminal end of the target proteinand used for purification according to the present invention.

The expression “Target protein” means the ultimate protein of interest.Thus the target protein may be the expressed fusion protein or, moretypically, it will be protein isolated after the purification tag hasbeen cleaved of.

The expression “Fusion protein” or “tagged” protein” means a proteinhaving a purification tag attached to either the C-terminal or theN-terminal end of the target protein.

“hGH” mean mature human growth hormone consisting of the 1-191 aminoacids in human growth hormone.

“hGH-Leu-Ala mean mature human growth hormone with a C-terminal Leu-Alaextension

With the expression “a highly basic protein” is meant a protein having ahigh percent of the basic amino acid residues Lys and Arg, e.g. at leastabout 15% of the total number of amino acid residues in the protein.

“Application” means a sample containing the fusion protein which isloaded on a purification column.

“Flow through” means the part of the application containing host cellproteins and contaminants which do not bind to the purification column

“Main peak” refers to the peak in a purification chromatogram which hasthe highest UV intensity and which contains the fusion protein

“mAU” is milliabsorbance units.

“UV 280 intensity” is the absorbance at a wavelength of 280 nm at whichproteins will absorb, measured in milliabsorbance units

“IPTG” is isopropyl-β-D-thiogalactopyranoside.

EK is enterokinase

TIC is Total Ion Count

With the expression “linker” is meant an amino acid sequence linking thepurification tag and the target protein together. The linker sequencemay comprise a sequence which promotes better folding of the targetprotein and/or a cleavage site for cleaving off the purification tag.

A “helix structure” is characterized by having an amino acid sequencewhich results in a coiled structure stabilized by interchain hydrogenbonds.

The expression “protein” will cover both peptides and polypeptides.

“% Solubility” is defined as the amount of soluble fusion protein fromhost cell lysate divided by amount of soluble+insoluble fusion proteinfrom host cell lysate×100.

“% Purity” is defined as the amount of the protein of interest dividedby the amount of protein of interest+the amount of host cellcontaminants×100.

SOE PCR means Splicing by overlap extension PCR.

LC-MS refers to liquid chromatography mass spectrometry.

In the present context, the term “functional analogue” is meant toindicate a protein with a similar function as the fusion protein nativeprotein. The protein may be structurally similar to the native proteinand may be derived from the native protein by addition of one or moreamino acids to either or both the C- and N-terminal end of the nativeprotein, substitution of one or more amino acids at one or a number ofdifferent sites in the native amino acid sequence, deletion of one ormore amino acids at either or both ends of the native protein or at oneor several sites in the amino acid sequence, or insertion of one or moreamino acids at one or more sites in the native amino acid sequence. Thusan insulin analogue is an insulin molecule having one or more mutations,substitutions, deletions and or additions of the A and/or B amino acidchains relative to the human insulin molecule. The insulin analogues arepreferably such wherein one or more of the naturally occurring aminoacid residues, preferably one, two, or three of them, have beensubstituted by another codable amino acid residue. Thus position 28 ofthe B chain may be modified from the natural Pro residue to one of Asp,Lys, or Ile. In another embodiment Lys at position B29 is modified toPro; Also, Asn at position A21 may be modified to Ala, Gln, Glu, Gly,His, Ile, Leu, Met, Ser, Thr, Trp, Tyr or Val, in particular to Gly,Ala, Ser, or Thr and preferably to Gly. Furthermore, Asn at position B3may be modified to Lys. Further examples of insulin analogues are des(B30) human insulin, insulin analogues wherein PheB1 has been deleted;insulin analogues wherein the A-chain and/or the B-chain have anN-terminal extension and insulin analogues wherein the A-chain and/orthe B-chain have a C-terminal extension. Thus one or two Arg may beadded to position B1.

Also, precursors or intermediates for other proteins may be purified bythe method of the invention. An example of such a precursor is aninsulin precursor which comprises the amino acid sequenceB(1-29)-AlaAlaLys-A(1-21) wherein A(1-21) is the A chain of humaninsulin and B(1-29) is the B chain of human insulin in which Thr(B30) ismissing.

Human growth hormone analogues may be Ser-hGH or hGH-Leu-Ala. GLP1analogues may be K34R-GLP-1(9-37) and GLP2 analogues may beGly²-GLP-2(1-33) or Lys¹⁷Arg³⁰-GLP-2(1-33).

In the present context the three-letter or one-letter indications of theamino acids have been used in their conventional meaning as indicated intable 1. Unless indicated explicitly, the amino acids mentioned hereinare L-amino acids. Further, the left and right ends of an amino acidsequence of a peptide are, respectively, the N- and C-termini unlessotherwise specified.

TABLE 1 Abbreviations for amino acids: Amino acid Tree-letter codeOne-letter code Glycine Gly G Proline Pro P Alanine Ala A Valine Val VLeucine Leu L Isoleucine Ile I Methionine Met M Cysteine Cys CPhenylalanine Phe F Tyrosine Tyr Y Tryptophan Trp W Histidine His HLysine Lys K Arginine Arg R Glutamine Gln Q Asparagine Asn N GlutamicAcid Glu E Aspartic Acid Asp D Serine Ser S Threonine Thr T

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference in theirentirety and to the same extent as if each reference were individuallyand specifically indicated to be incorporated by reference and were setforth in its entirety herein (to the maximum extent permitted by law).

All headings and sub-headings are used herein for convenience only andshould not be construed as limiting the invention in any way.

The use of any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

The citation and incorporation of patent documents herein is done forconvenience only and does not reflect any view of the validity,patentability, and/or enforceability of such patent documents.

This invention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw.

EXAMPLES Example 1 Cloning and Expression of hGH in E. coli Fused to thePurification Tag SEQ ID NO:1 and Different Linkers

1. Cloning

SEQ ID NO:1 is the 30S ribosomal protein S21 derived from sequencedgenome of the thermophile Bacillus stearothermophillus. The molecularweight of the tag was calculated to 6.7 kDa and the pl of the tag wascalculated to 11.3. When fused to human hGH the fusion protein (NNC20)including the linker with SEQ ID NO:6 will have a molecular weight of29.9 kDa and a pl of 9.2.

The rpsU gene encoding the purification tag was codon optimized forexpression in E. coli. The tag was assembled from 6 different primerscovering the entire gene sequence by splicing by overlap extension(SOE). Two consecutive rounds of PCR were performed.

In the first reaction all 6 primers were allowed to assembly in astandard PCR reaction using 15 cycles and a lowered annealingtemperature of 50° C. The PCR conditions were as follows using thePyrobest polymerase system (Takara):

95° C.: 3 min. (denaturing)

94° C.: 45 sec (denaturing)

50° C.: 45 sec (annealing)

72° C.: 45 sec (extension)

15 cycles

72° C.: 10 min

For the second PCR reaction a 1/50 dilution of the PCR product from thefirst reaction was used as template and the primers comprising the 5′and 3′-ends of the gene were used to amplify the full length tag. ThePCR conditions for the 2. PCR reaction was the same as for the first,except that the annealing temperature was increased to 54° C. and thenumber of cycles to 25.

The terminal 5′-end forward primer matching the 5′-end of the rspU genewas designed with a NdeI restriction enzyme cleavage site and theterminal 3′-reverse primer comprised a SacII site. The NdeI and SacIIsite were chosen as they could be used as cloning sites for ligation ofthe purification tag sequence into a pET11a expression vector (Novagen)already comprising human growth hormone encoding sequence with aN-terminal ubiquitin tag and a linker containing a SacII site in frontof the enterokinase cleavage site DDDDK (SEQ ID NO:10).

The second PCR product was purified from a clear band on an agarose geland cleaved with NdeI and SacII restriction enzymes. The pET11aexpression vector was also cleaved with NdeI and SacII. Ligation of thelinarized vector with the RS21_BACST insert using T4-ligase yields aconstruct encoding the RS21_BACST tag linked to mature hGH with anintervening RRGGSDDDDK (SEQ ID NO:6) linker. The ligation product wastransformed into E. coli JM109 on LB-ampicillin plates. Colonies onplates were propagated overnight and plasmids from these were isolatedby standard mini prep methods and were evaluated for the presence of thepurification tag insert by means restriction enzyme cleavage with NdeIand SacII. Plasmids with the correct cleavage pattern were DNAsequenced. Plasmids with the correct DNA sequence were transformed intoE. coli expression strain BL21, which were plated on LB/ampicillinplates overnight, respectively.

Other pET11a expression vectors encoding variants of hGH fusion proteinswith different linker regions were created. In general, this wasaccomplished by removal of the linker SEQ ID NO:6 regions with suitablerestriction cleavage enzymes and ligation with double stranded oligosencoding the new linker region. The oligoes were obtained by annealingof two complementary oligoes encoding the new linker and which hadcohesive ends compatible with those in the linearized vector. Thefollowing fusion hGH constructs were cloned:

Product name Tag Linker NNC20 SEQ ID NO: 1 SEQ ID NO: 6 NNC20.1 SEQ IDNO: 1 SEQ ID NO: 7 NNC20.2 SEQ ID NO: 1 SEQ ID NO: 8 NNC20.3 SEQ ID NO:1 SEQ ID NO: 92. Expression in E. coli BL21

E. coli BL21 cells transformed with plasmids encoding fusion constructsof hGH were grown to a OD600 of ˜0.6 at 37° C. The temperature was thenlowered to 25° C. for approximately 30 min, and 0.5 or 1 mM IPTG wasadded to the culture for 3 hours. Cells were then harvested bycentrifugation. SDS-PAGE analysis could visualize that an hGH fusionprotein of the correct size could be induced in E. coli. Comparisonbetween the different constructs with showed differences in the amountof full length fusion protein that could be obtained after inductionwith IPTG. Thus NNC20.3 was expressed in a higher yield than observedfor NNC20, NN20.1, NN20.2 and NN20.2.

NNC20 and NNC20.3 were >80% soluble when induced for 3 hours at 25° C.and had an Mw of ˜30 kDa as calculated from the amino acid sequence.

3. Purification of NNC20

Initially, a binding assay using pellets dissolved in different bufferswith different salt concentrations and pH showed that the fusion proteinefficiently bind to SP sepharose FF matrix (Amersham Pharmacia) up to apH of 9 and at salt concentration of up to 0.3 M NaCl. This indicatesthat the SEQ ID NO:1-hGH protein can be purified at conditions whereonly very few other proteins should be able to bind the matrix.

Pellet from 80 ml culture of E. coli BL21 expressing NNC20 was sonicatedin 25 mM sodium phosphate, 5 mM EDTA pH 8 and cell debris was removed bycentrifugation. After sonication NaCl was added to a final concentrationof 0.3 M to decrease the ability of E. coli contaminants to bind to thecation exchange matrix and the application was sterile filtrated.Purification was done on an AKTA explorer (Amersham Pharmacia) with aflow rate of 0.5 ml/min. The following buffers were used:

Buffer A: 25 mM sodium phosphate, 5 mM EDTA, pH8, 0.3M NaCl

Buffer B: 25 mM sodium phosphate, 5 mM EDTA, pH8, 1M NaCl,

Buffer C: 2M NaCl

The prepacked SP FF (HR5/5) column (Amersham Pharmacia) was equilibratedwith buffer A for 5 column volumes (CV). The application containingNNC20 was loaded on the column and unbound sample was washed out withbuffer A for 20 CV. A gradient from 0-50% buffer B was used for 20 CV.Finally an isocratic step using buffer C for 10 CV was used to elute thetarget protein from the column.

Fractions containing the eluted fusion protein were collected and thepurity of the fusion protein present in the NNC20 main peak of thechromatogram was evaluated by SDS-PAGE image analysis. Coomasie stainedSDS PAGE gels of the fraction covering the NNC20 main peak estimated thepurity of the protein to be >90% FIG. 2 shows the fractions collectedfrom the NNC20 main peak, which contains the fusion protein run on aSDS-PAGE gel at non-reducing conditions.

4. Purification of NNC20.3

NNC20.3 was expressed in E. coli BL21 as described for pNNC20 exceptthat only 0.5 mM IPTG used to induce the fusion protein. Pellet from 40ml of culture was dissolved to an OD600 of 5 in 25 mM sodium phosphatebuffer pH 7 and cell debris was removed by centrifugation. The resultingsupernatant was sterile filtrated and purified on the AKTA explorer at aflow rate of 0.5 ml/min using the following buffers:

Buffer A: 25 mM sodium phosphate pH 7

Buffer B: 25 mM sodium phosphate pH 7 and 1 M NaCl

A 1 ml column packed manually with SP FF matrix (Amersham Pharmacia) wasequilibrated with buffer A for 5 column volumes (CV). The applicationcontaining NNC20.3 was loaded on the column and unbound sample waswashed out with buffer A for 7 CV. A gradient from 0-100% buffer B wasused for 20 CV during which the fusion protein was eluted at a NaClconcentration of approximately 0.5 M. The purity of the fusion proteinpresent in the main peak was estimated to be approximately 90% using theImageJ analysis software (Rasband, W. S., ImageJ, U.S. NationalInstitutes of Health, Bethesda, Md., USA, http://rsb.info.nih.gov/ij/,1997-2005). FIG. 3A shows a chromatogram showing the elution of NNC20.3at approximately half maximal conductivity.

Fraction 13 and 14 representing a volume of ˜3 ml were pooled anddigested with 0.01 U/ml of recombinant bovine enterokinase light chainfor 6 hours at room temperature. SDS PAGE showed that the ˜30 kDa fusionprotein band almost disappeared and a band of ˜22 kDa corresponding tomature hGH without the purification tag appeared as well as a band of ˜6kDa representing the released purification tag. The digested sample wasthen diluted ˜5 times in 25 mM sodium phosphate pH 7, 10 mM PMSF buffer(PMSF was added to minimize previously described unspecific EK cleavagein the hGH sequence). This was done in order to lower the saltconcentration, so that the highly basic protein co-eluting with thefusion protein in the first run as well as the purification tag releasedby EK would efficiently bind the cation exchange column in the secondrun. The diluted sample was run using the SP FF column with sameparameters as described above. The flow through was collected andup-concentrated using a Vivaspin 15 ultrafiltration column (Vivascience)a 3000 rpm until the volume was reduced ˜5 times. SDS-PAGE analysis ofthe up-concentrated flow through sample showed that it containedessentially pure mature hGH, only contaminated with small amounts of hGHfragments coming from unspecific cleavage due to EK. The released tag,remaining uncleaved fusion protein and contaminants co-eluting withNNC20.3 in the first step is thus retained on the cation-exchange columnin the second purification step.

Other data prove that the fusion proteins can be expressed withoutsignificant degradation of the purification tags measured as indicatedby Coomasie stained PAGE gels or by Western Blotting. Also upon peptidemass mapping using MALDI mass spectrometry of SEQ ID NO:1-hGH constructsonly very few peptides were found after cleavage with trypsin,altogether indicating high resistance of the tag towards trypsin-likeproteases. MALDI analysis of disulphide bridges in SEQ IDNO:1-hGH(NNC20.3) also indicated that the SEQ ID NO:1-tag did notinterfere with the establishment of the correct disulphide bridges inthe hGH target protein.

In the binding assay evaluating the binding of NNC20 expressed in E.coli, to SP sepharose fast flow matrix at different salt concentrationsand buffers it was observed that the fusion protein efficiently binds toSP sepharose up to pH 9 and at salt concentration up to 0.3 M NaCl.

Example 2 Cloning and Expression of Fusion Constructs of SEQ ID NO:2,SEQ ID NO:15 and hGH in E. coli

SEQ ID NO:2 is the 30S ribosomal protein L39 derived from the sequencedgenome of the thermophile Archaeoglobus fulgidus

The molecular weight of the purification tag was calculated to 5.9 kDaand the pl of the tag was calculated to 12.5. When fused to human hGHthe fusion protein will have a molecular weight of 29.2 kDa and a pl of9.5. The rpl39e gene encoding the tag was codon optimized for expressionin E. coli. The tag was assembled from 6 different primers covering theentire gene sequence by splicing by overlap extension (SOE) PCR. Twoconsecutive rounds of PCR were used essentially as described for pNNC20in example 1. The 5-end primer matching the 5′-end of the rpl39e genewas designed with a NdeI restriction enzyme cleavage site and theterminal reverse primer comprised the 3′-end of the rpl39e gene andoverhang comprising a NheI site. PCR product was subcloned into thepCR2.1 TOPO vector according to the manufactures instructions(Invitrogen) and the sequence was verified by DNA sequencing. Thepurification tag part was cut out of the TOPO vector and ligatedtogether with a purified pNNC20.3 vector linearized with NdeI and NheIusing the Rapid ligation Kit (Roche). The ligation product wastransformed into E. coli TOP10 for amplification of the new plasmidovernight by plating on LB/ampecillin plates. Plasmids from overnightcolonies were obtained and were evaluated by means restriction enzymecleavage and DNA sequencing. A clone comprising the correct fusionproduct consisting of SEQ ID NO:2, SEQ ID NO:15 and hGH was isolated,transformed into E. coli expression strain BL21 and expressed at 25° C.for 3 hours using 0.5 mM IPTG as described in Example 1. SDS-PAGE showedthat the construct yielded a fusion protein of the correct size of ˜30kDa, which was approximately 80% soluble.

Pellets of the expressed fusion product of SEQ ID NO:2, SEQ ID NO:15 andhGH from 40 ml culture was sonicated in 20 mM KPO₄ pH 7, 0.1% TritonX-100 and cell debris was removed by centrifugation. The resultingsupernatant was sterile filtrated and purified using the AKTA explorerat a flow rate of 1 ml/min with the following buffers:

Buffer A: 20 mM potassium phosphate pH 7

Buffer B: 20 mM potassium phosphate pH 7 and 1 M NaCl

A 1 ml column packed manually with SP FF matrix (Amersham Pharmacia) wasequilibrated with buffer A for 5 column volumes (CV). The applicationcontaining the tagged hGH was loaded on the column and unbound samplewas washed out with buffer A for 5 CV. A gradient from 0-100% buffer Bwas used for 20 CV during which the target protein was eluted. Thepurity of the target protein present in the main peak was estimated tobe approximately 90%. FIG. 3B is a chromatogram showing the elution ofthe fusion product of SEQ ID NO:2, SEQ ID NO:15 and hGH at approximately0.8 M NaCl.

Example 3 Cloning of hGH Leu-Ala Variants

The C-terminal of hGH in the fusion protein described in Example 1(NNC20.3) was extended with Leu-Ala. In short, PCR amplification wascarried out with a forward primer spanning a Bsu361 site 300 bp from thestop codon in hGH encoding sequence of pNNC20.3. The reverse primer hadtwo extra codons encoding Leu-Ala before the stop codon terminating themature hGH sequence and a 5′-end BamHI cloning site. The template usedwas pNNC20.3. This PCR product was purified using the GFX PurificationKit (Amersham Pharmacia) and cloned into the pCRIITOPO vector(Invitrogen) and sequenced. Insert with correct sequence was excisedwith Bsu361 and BamHI and ligated into pNNC20.3 cleaved with Bsu361 andBamHI. This yields a SEQ ID NO:1-SEQ ID NO:9-hGH-Leu-Ala constructpACSH74.

A number of purification tags (SEQ ID NO: 20 to 42) have been tested forexpression levels, solubility and purification potential. These tags arederived from genes encoding 23 different highly basic ribosomal proteinswere PCR amplified from genomic DNA of Thermotoga maritima (obtainedfrom American Type Culture Collection, ATCC 43589).

In short, an NdeI cloning site was included in the forward primerimmediately upstream of the start codon of the ribosomal proteinencoding sequence. An XhoI cloning site was included to the reverseprimer after the codon encoding the last aa of the ribosomal proteinencoding sequence. The PCR products were purified from agarose gels andcloned into the pCRII TOPO vector. NdeI/XhoI inserts with correctsequence were exicised from TOPO clones ligated into an pACSH74, thusreplacing the SEQ ID NO:1. All constructs have the linkerSSSSTLAAPFDDDDK (SEQ ID NO:9) between the N-terminal tag and the startphenylalanine of the hGH-Leu-Ala sequence.

The following hGH-Leu-Ala fusion proteins were cloned:

Product name Tag Linker ACSH74 SEQ ID NO: 1 SEQ ID NO: 9 ACSH118 SEQ IDNO: 20 SEQ ID NO: 9 ACSH119 SEQ ID NO: 21 SEQ ID NO: 9 ACSH120 SEQ IDNO: 22 SEQ ID NO: 9 ACSH121 SEQ ID NO: 23 SEQ ID NO: 9 ACSH122 SEQ IDNO: 24 SEQ ID NO: 9 ACSH123 SEQ ID NO: 25 SEQ ID NO: 9 ACSH124 SEQ IDNO: 26 SEQ ID NO: 9 ACSH125 SEQ ID NO: 27 SEQ ID NO: 9 ACSH126 SEQ IDNO: 28 SEQ ID NO: 9 ACSH127 SEQ ID NO: 29 SEQ ID NO: 9 ACSH128 SEQ IDNO: 30 SEQ ID NO: 9 ACSH129 SEQ ID NO: 31 SEQ ID NO: 9 ACSH130 SEQ IDNO: 32 SEQ ID NO: 9 ACSH131 SEQ ID NO: 33 SEQ ID NO: 9 ACSH132 SEQ IDNO: 34 SEQ ID NO: 9 ACSH133 SEQ ID NO: 35 SEQ ID NO: 9 ACSH134 SEQ IDNO: 36 SEQ ID NO: 9 ACSH135 SEQ ID NO: 37 SEQ ID NO: 9 ACSH136 SEQ IDNO: 38 SEQ ID NO: 9 ACSH137 SEQ ID NO: 39 SEQ ID NO: 9 ACSH140 SEQ IDNO: 40 SEQ ID NO: 9 ACSH142 SEQ ID NO: 41 SEQ ID NO: 9 ACSH143 SEQ IDNO: 42 SEQ ID NO: 9Expression of hGH-Leu-Ala Constructs in E. coli and Binding Assay:

23 hGH-Leu-Ala constructs with purification tags amplified fromThermotoga maritima were transformed into Rosetta (DE3) strain. Cellswere grown to a OD600 of ˜0.4-0.6 at 37° C. Then the temperature waslowered to 30° C. for approximately 30 min and 0.5 IPTG was added to theculture for 3 hours. All constructs gave a clear protein band of theexpected size. Expression levels differed somewhat between constructs.They all showed a solubility of between about 50% to more than 80% aftersonication in 10 mM phosphate buffer.

Six candidates were tested for their affinity for binding SP FF on smallcolumns loaded with 0.75 ml SP FF matrix. The Method used was asfollows:

Buffer A: 25 mM Na₂HPO₄ NaH₂PO₄ pH 7

Buffer B1: 25 mM Na₂HPO₄ NaH₂PO₄ pH 7 0.5 M NaCl

Buffer B2: 25 mM Na₂HPO₄ NaH₂PO₄ pH 7 1 M NaCl

1) Wash columns with 5 ml water, 2 ml buffer A, 3 ml buffer B2

2) Equilibrate in 6 ml buffer A

3) Load cell supernatants and collect flow through (FT)

4) Wash with 3 ml of buffer A and collect FT

5) Elute with 2 ml buffer B1 and collect FT

6) Elute with 2 ml buffer B2 and collect FT

ACSH122 and ACSH200 were almost completely eluted with 0.5 M NaCl andACSH198, ACSH199 and ACSH74 were eluted with both 0.5 and 1 M NaCl,indicating stronger interaction with the column. No fusion protein atall was observed in the flow through for ACSH74, whereas the rest showeddifferences in the binding efficiency.

AKTA Purification of ACSH74, ACSH130 and ACSH131:

Purification of ACSH 74

ACSH74 was expressed in BL21 (DE3) and purified as described for NN20.3in example 1. The results were almost identical with those obtained forNN20.3 indicating that the Leu-Ala extension in the C-terminal did notinfluence the binding of the tag to the SP FF

Purification of ACSH130 and ACSH131:

Pellets from 40 ml of culture were sonicated in 25 mM NaPO₄ pH 7 asdescribed in example 1. Purification was done on an AKTA explorer(Amersham Pharmacia) with a flow rate of 5 ml/min using a HiTrap5 ml SPFF column (Amersham Pharmacia) and the following buffers:

Buffer A: 25 mM sodium phosphate, pH 7

Buffer B: 25 mM sodium phosphate, pH 7+1M NaCl

The column was equilibrated with buffer A for 5 column volumes (CV). Theapplication containing ACSH131 or ACSH130 was loaded on the column andunbound sample was washed out with buffer A for 7 CV. A gradient from0-100% buffer B was used for 20 CV. ACSH131 and ACSH130 was eluted fromthe column with approximately 50% Buffer B (0.5 NaCl). For both ACSH131and ACS130 binding to SP FF was less efficient than observed for NN20,NN20.3 and ACSH74, but the purity was at a similar high level.

Example 4 Cloning of Insulin Antagonist S661 Fusion Proteins

S661 is a insulin receptor antagonist The peptide comprises onedisulphide bridge and has the following sequence:

SEQ ID NO: 43: GSLDESFYDWFERQLGGGSGGSSLEEEWAQIQCEVWGRGCPSYThe nucleotide sequence of S661 sequence was codon optimized for optimalexpression in E. coli. A XhoI site and BamHI cloning site was includedin the 5′ end and 3′-end of the S661 sequence to enable easy cloninginto existing hGH-Leu-Ala constructs (Example 3). The S661 sequence wassynthesized by Splicing by overlap extension PCR as describedpreviously. In short, 3 forward primers and 3 reverse primers of ˜50 bpin length were designed cover the S661 sequence with XhoI/BamHI cloningsites with overlaps of approx 20 bp. The linker encoding SSSSDDDDK (SEQID NO:16 was added between the purification tags and S661.Two rounds of PCR was performed as using the Phusion PCR Kit (Finnzymes)at conditions recommended by the manufacturer.The first PCR reaction had the following conditions:98° C. 30 sec,98° C. 10 sec (denaturation)50° C. 30 sec (annealing)72° C. 15 sec (elongation)10 cycles72° C. 5 minFirst PCR product was excised from 2% agarose gels and purified by GFXkit (GE Health care), diluted 1/50 and use as template for the last PCRreaction. The second PCR reaction was performed with the most terminaltwo primers comprising the XhoI and BamHI cloning sites using the sameconditions as for the first reaction except that 55° C. was used asannealing temperature and 15 cycles was used. A band of the expectedsize was excised from 2% agarose gels, purified by GFX kit (GE HealthCare) and ligated into pCRIITOPO vector (Invitrogen) as described by themanufacturer. A clone with correct sequence was isolated and the S661insert was released with XhoI and BamHI and ligated into the vector partof different hGH-Leu-Ala constructs from which hGH-Leu-Ala had beenexcised with XhoI/BamHI. This yielded the following constructs withdifferent purification tags N-terminal linked to the S661 sequence withdifferent linkers:

Product name Tag Linker ACSH197 SEQ ID NO: 24 SEQ ID NO: 16 ACSH198 SEQID NO: 31 SEQ ID NO: 16 ACSH199 SEQ ID NO: 32 SEQ ID NO: 16 ACSH200 SEQID NO: 33 SEQ ID NO: 16Expression of ACSH197-ACSH200pACSH197-ACSH201 was transformed into Rosetta (DE3) (Novagen), whichwere cultivated in the presence of Ampecillin and Chloramphinicol asdescribed by the manufacteror. Cells were grown to a OD600 of ˜0.4-0.6at 37° C. The temperature was then lowered to 30° C. for approximately30 min. Protein synthesis was then induced with 0.5 mM IPTG for 3 hoursat 30° C. Cell with induced protein were harvested by centrifugation.SDS evaluation showed that all constructs expressed a protein of theexpected size, with minor differences in expression levels andsolubility.Purification of ACSH200

Cells from 40 ml culture of E. coli Rosetta (DE3) from a 3 hourexpression of ACSH200 in 200 ml medium (final OD 600=1.6) at 30° C. wassonicated in 10 ml 25 mM sodium phosphate pH 8.5, cell debris wasremoved by centrifugation and the application was sterile filtrated anddiluted to 20 ml with 25 mM sodium phosphate buffer. The solubilitywas >80% for this fusion protein. Purification was done on an AKTAexplorer (Amersham Pharmacia) with a HiTrap SP-FF, 5 ml column with a 5ml/min flow rate. The following buffers were used:

Buffer A: 50 mM sodium phosphate, pH 8.5

Buffer B: 50 mM sodium phosphate, pH 8.5+1 M NaCl

A 5 ml SP FF (HR5/5) column (Amersham Pharmacia) was equilibrated withbuffer A for 5 column volumes (CV). The application containing ACSH200was loaded on the column and unbound sample was washed out with buffer Afor 5 CV. A gradient from 0-100% buffer B was used for 20 CV. ACSH200was eluted at approximately 30% buffer B (0.3 M NaCl) (FIG. 3A).Fractions containing the eluted fusion protein were collected and thepurity of the fusion protein present in the main peak of thechromatogram was evaluated by SDS-PAGE (FIG. 3B) and software analysis.No protein was detected in the flow through indicating that all proteindid bind the SP FF column. Coomasie stained SDS PAGE gels of thefraction covering the ACSH200 main peak estimated the purity of theprotein to be ˜90%. A similar purification was performed at pH 7, whichgave the same mAU signal (but somewhat less purity) indicating thatrecovery of the purified protein is not affected by pH 8.5 of thebuffer. This is advantages as less contaminant protein can bind thecolumn at pH 8.5.LC-MS Analysis of Fraction 25 from Purification of ACSH200Fraction 25 from purification was diluted 1:1 with sodium phosphatebuffer and 20 uL was analyzed on a LC-MSD_TOF (Agilent technologies)instrument using an analytical Poroshell 300SB-C8, Micro Bore 1.0×75 mm,5 micron (Agilent Technologies) column at standard HPLC conditions witha flow of 0.3 ml/min and a column temperature of 70° C.: A gradientelution was formed in a 20 min. run using 8.8 mM ammonium formate in0.1% formic acid water (Buffer A) and Acetonitrile (Buffer B) asfollows:

Time (min) % Buffer B 0 22 3 22 15 75 15.1 90 20 90MS Settings were as Recommended by the ManufacturerThe TIC (total ion count) chromatogram obtained by LC-MS analysispredominantly showed one peak. The extracted deconvoluted spectrum ofthis peak showed a peak with the mass of 14810.41 Da very close to thepredicted mass of 14810.45 Da of ACSH200 without the N-terminalmethionine (which is removed by E. coli methionine amino peptidase)(FIG. 4C). The molecular mass of the fusion protein changed with ˜2 Daupon 1 hour treatment with 50 mM DTT. Altogether this suggests that thedisulphide bridge is correctly established in the protein, which showsthat the RL27_THEMA (SEQ ID NO:33) tag does not interfere with correctestablishment of the disulphide bridge.Purification of ACSH 199 and ACSH 198

Purification of ACSH199 and ACSH198 was performed as described in forACSH200.

ACSH199 and ACSH198 were eluted at approximately 50% buffer B (0.5 MNaCl), and showed less efficient binding to the column as protein wasobserved in the flowthrough. However, for both constructs the purity offusion proteins in eluted fractions was comparable with that of ACSH200

Example 5 Thermoprecipitation of E. coli Contaminants

With ACSH200 as model protein it was investigated whether E. colicontaminants could be heat-precipitated at high temperatures, while thefusion protein due to the thermostability of the tag could be retainedin solution.

ACSH200 was expressed as described in Example 4. Pellets were dissolvedin 25 mM sodium phosphate pH 7 and sonicated as described above. From 10mM-1 M NaCl was added to the supernatant. The samples were heated for70° C. for 30 min and immediately cooled on ice for 10 min. Samples werethen centrifuged for 10 min. at 15.000 G and the supernatants werecompared to a non-heated control using SDS PAGE. Significant amounts ofespecially high abundant E. coli contaminants could be removed withincreasing NaCl conc. (FIG. 5). The heat precipitation did not affectthe recovery of the target protein compared to the non-heated controlindicating that the claimed purification tags do facilitate a precolumnpurification step with thermo precipitation. Same efficiency ofprecipitation was obtained with this strategy using pH 8.5 in thebuffer, indicating that the high pH can be combined with thermoprecipitation, thus improving the starting material for cation exchangepurification.

Example 6 Cloning of Human Amylin Fused to Purification Tags

Human amylin is a small peptide hormone comprising 37 aa:

SEQ ID NO: 44: KCNTATCATQRLANFLVHSSNNFGAILSSTNVGSNTY

The nucleotide sequence of the human amylin sequence was codon optimizedfor optimal expression in E. coli. The coding sequence was generated bySOE PCR using 6 primers of ˜50 bp in length with ˜20 bp overlapscovering the entire human amylin sequence. The same general methodologyand cloning sites (XhoI/BamHI) were used as described for S661 inExample 4. The following constructs were cloned:

Product name Tag Linker ACSH202 SEQ ID NO: 24 SEQ ID NO: 16 ACSH203 SEQID NO: 31 SEQ ID NO: 16 ACSH204 SEQ ID NO: 32 SEQ ID NO: 16 ACSH205 SEQID NO: 33 SEQ ID NO: 16Expression of ACSH202-205:

Expression was carried out as described for S661 constructs in Example4. Protein bands of correct size were obtained for all constructs.Double bands were observed for ACSH202, ACSH203 and LC-MS analysisindicated cleavage by unknown E. coli proteases in the amylin sequence.

Purification of ACSH204 and Enterokinase Digestion of ACSH204:

Purification of ACSH204 was performed as described above using a bufferA and buffer B as described in example 4, but at pH 7. Fractions werecollected and analysed. To evaluate whether EK can release human Amylinfrom the purification tag, 2 ml of the purest fraction of RL23_AMYrepresenting the major peak was upconc. in Vivaspin 2, CTA 5000 Da MWCO(Vivascience, Satorius) to 1 ml and diluted 1:1 in 500 mM Tris HCl pH 7,10 mM CaCl2. 0.003 U/uL EK was added to 400 uL reaction volume andincubated for 1 h at 37° C. The sample was analyzed with LC-MS asbriefly described in Example 4 and the TIC chromatogram showed fourdistinct peaks (FIG. 6A). Extracted spectra of peak 1 showed the mass ofhuman Amylin in 3 (1309.56×3-22 Da (Na adduct)-3H⁺=3903.7, 4 (982.42Da×4-22 Da (Na adduct)-4H⁺=3903.7) or 5 charge states (781.74Da×5-5H⁺)=3903.7 (FIG. 6 b). The mass of 3903.7 Da closely matched thetheoretical average isotopic mass of human amylin with an intactdisulphide bridge: 3904.3 Da.

Peak 2 in the TIC chromatogram was clearly the most abundant and theextracted deconvoluted spectrum showed a predominant peak correspondingin mass to the released purification tag (SEQ ID NO:32-SEQ ID NO:16,12764,84 Da, average isotopic mass, calculated) (FIG. 6C). The extracteddeconvoluted spectrum of Peak 3 showed the mass of the intactunprocessed ACSH204 fusion protein (16561, 1 Da average isotopic mass,calculated). The peak size of the amylin peptide on the TIC chromatogramdoes not correspond to the size of the released SEQ ID NO:32-SEQ IDNO:16 tag, which is possibly due to less binding of the peptide to theC8 column, differences in ionization efficiency or aggregation ofreleased amylin after released from the tag.

Our data shows that, it is possible to make human Amylin in soluble formthat can purified and processed with EK using basic thermostablepurification tags.

The invention claimed is:
 1. A method for purification of a recombinanttarget protein expressed in a eukaryotic or prokaryotic host cellcomprising: (a) isolating an expressed tagged protein from the hostcell, wherein the expressed tagged protein comprises a target protein,the purification tag of SEQ ID NO: 33, and a linker sequence comprisinga cleavage site for in vitro cleavage of the target protein from thepurification tag; (b) subjecting the expressed tagged protein tocation-exchange chromatography purification; (c) cleaving the targetprotein from the purification tag; and (d) isolating the target protein.2. The method according to claim 1, wherein the linker has from 1 toabout 15 amino acid residues.
 3. The method according to claim 1,wherein the linker has from 1 to about 30 amino acid residues.
 4. Themethod according to claim 1, wherein the linker comprises amino acidresidues selected from the group consisting of Pro, Leu and Ala.
 5. Themethod according to claim 1, wherein the linker comprises a cleavagesite which is selected from the group consisting of an enterokinasecleavage site, a Factor Xa cleavage site, a thrombin cleavage site, aTobacco etcs virus protease cleavage site and a HRV14 3C proteasecleavage site.
 6. The method according to claim 1, wherein the linkerhas a peptide selected from the group consisting of SEQ ID NO: 6, SEQ IDNO: 7, SEQ ID NO: 8, SEQ ID NO: 9, and SEQ ID NO:
 15. 7. The methodaccording to claim 1, wherein the host cell is selected from bacteria orfungi.
 8. The method according to claim 1 further comprising a heatprecipitation step for precipitating thermolabile host cell contaminantsbefore the cation-exchange column in step (b).
 9. The method accordingto claim 1, wherein the target protein is human hGH or an analoguethereof.
 10. The method according to claim 9, wherein the target proteinis hGH-Leu-Ala or Ser-hGH.
 11. The method according to claim 8, whereinfrom about 30 to about 200 mM NaCl is added before the heatprecipitation step.
 12. The method of claim 1 wherein cleaving thetarget protein from the purification tag is accomplished by a suitableprocessing enzyme.
 13. The method according to claim 7, wherein the hostcell is selected from the group consisting of Eschericia sp., Bacillussp., Saccharomyces sp., and, Aspergillus sp.